i) births and deaths
12 May 1968: birth of Catherine Tate, who played Donna Noble in New Who from 2006 to 2010.
ii) broadcast anniversaries
12 May 1973: broadcast of sixth episode of Planet of the Daleks. The Doctor, Jo and the Thals trap the Daleks in the ice volcano.
12 May 1996: first broadcast of Doctor Who: The Movie on a local cable channel in Edmonton, Canada.
12 May 2007: no Doctor Who episode shown today, the series taking a break for the Eurovision Song contest between The Lazarus Experiment and 42.
iii) date specified in canon
12 May 1999: birth of Adelaide Brooke, who we meet in The Waters of Mars (2009).
It’s a good question – of course they’ve been circulating now for over a decade, so one might have thought that the mixing has reached saturation level.
The reason we don’t end up with homogenous mixtures of the coins in euro-land (and indeed that, who like me is in Belgium but much closer to the Dutch border, therefore has many more Dutch coins than I do) is that each country’s central bank takes in all other countries’ coins but only gives out their own. That means that at the core of every state you have a constant source of your own country’s coins priming the pump. Not surprisingly, a French study found that non-French coins are much more likely to be found in areas bordering other Euro-land countries (not Switzerland).